Special reactions of α,β-unsaturated ketones III.: Formation and structure elucidation of dimers of 2-arylmethyleneketones:: (5E)-5-benzylidene-9β-phenyl-trans-4a-1,2,3,4,4a,5,6,7,8,9a-decahydroxanthen-4aα-ol and 3β,5β-bis-(4-methoxyphenyl)-2α,4β,6α-trimethyl-4α-propionyl-cyclohexanone

The reaction of 2-benzylidenecyclohexanone and 1-(4-methoxyphenyl)-2-methyl-1-penten-3-one with guanidine did not yield the expected 4-phenylhexahydro-2-quinazolinamine and 4-(p-methoxyphenyl)-dihydro-2-pyrimidinamine, respectively, but nitrogen-free products which turned out as [3+3]- and [4+2]-cycloadducts of two molecules of the applied vinylogous ketone each. According to elemental analyses, mass spectra, and, in particular, NMR analyses (H-1 and C-13 NMR, HH-COSY, gs-HSQC, gs-HMBC, I D TOCSY, NOESY, and I D NOE difference spectra), the prepared dimers were identified as racemic (5E)-5-benzylidene-9 beta -phenyl-trans-4a-1,2,3,4,4a,5,6,7,8,9a-decahydroxanthen-4a alpha -ol and 3 beta ,5 beta -bis-(4-methoxyphenyl)-2 alpha ,4 beta ,6 alpha -trimethyl-4 alpha -propionylcyclohexanone, respectively. Structure and stereochemistry of the dimers are elucidated, and mechanisms for their formation are proposed.